1. Field of the Invention
The present invention relates to an oil-separator rotor for a turbomachine such as an airplane turboprop or turbojet.
2. Description of the Related Art
An oil-separator rotor of that type comprises a tubular hub defining an internal axial duct for passing fluid and including an outer annular collar, together with an annular cap of substantially L-shaped section that is mounted around the hub. The cap has a radial wall that is parallel to the collar of the hub and that is connected at its outer periphery to one of the axial ends of a cylindrical wall that extends axially as far as the outer periphery of the collar.
The cap co-operates with the collar of the hub to define an annular chamber that is in fluid flow communication with the internal passage of the hub via radial slots therein. Means for depositing oil by centrifuging are housed in the chamber.
The oil-separator rotor is mounted on an element of the rotor of the turbomachine, in general at the downstream end of a degassing tube, and it serves to separate the oil and the air of an air/oil mixture, said oil then being recovered by suitable means in order to be recycled. The air/oil mixture is in the form of an oil mist, i.e. air having droplets of oil dispersed therein in suspension. Oil separation is obtained in particular by centrifuging the oil under the effect of the oil-separator rotor rotating.
In one particular configuration, while the turbomachine is in operation, the air/oil mixture flows inside the degassing tube and penetrates into the internal passage of the hub of the oil-separate rotor via its upstream end. Under the effect of centrifugal forces, the droplets of oil are urged radially outwards. When they reach the radial slots in the hub, they pass through the slots by centrifuging and then penetrate into the annular chamber of the oil-separator rotor, in which they are forced to become deposited on the oil deposition means housed in the annular chamber. The oil is then evacuated radially outwards through the openings in the cylindrical wall of the cap, and the air separated from the oil leaves via the downstream end of the internal passage of the hub.
A known oil-separator rotor has its cap fastened to the collar of the hub by screws that pass axially through the annular chamber housing the oil deposition means. Those screws pass through orifices in the radial wall of the cap and in the collar of the hub, and they are surrounded by spacers that isolate them from the oil deposition means. The cap fastener screws then extend through the annular space of the chamber occupied by the oil deposition means, thereby occupying said space and possibly disturbing oil recovery, since it is possible for the oil deposition means to be flattened to a greater or lesser extent by the screws.
Furthermore, the free end of the cylindrical wall of the cap bears radially inwards against the outer periphery of the collar. In this configuration, this free end of the cap forms means for centering the collar of the hub. In operation, under the effect of centrifugal forces, the free end of the cylindrical wall of the cap tends to become oval, by deforming locally outwards. Under such circumstances, there is a risk of uncontrolled oil leakage to the outside of the chamber.
An oil-separator rotor is also known in which the cap is fastened on the hub as an interference fit, the inner periphery of the radial wall of the cap clamping onto the hub. In order to avoid the above-mentioned problems associated with the downstream end of the cap ovalizing, said end is welded to the outer periphery of the collar via at least three weld beads that are regularly distributed around the longitudinal axis of the rotor.
Nevertheless, under such circumstances, the cap is fastened on the hub in such a manner that it is difficult to remove. Furthermore, it has been found that the weld beads are not a good solution to the above-mentioned problem, since they are subjected to high levels of stress concentration that cause cracking to appear in those beads. There is then a major risk of the cap becoming disengaged from the hub, with the interference fit of the cap possibly being found insufficient for retaining said part on the hub of the oil-separator rotor.
The cracked weld beads may be repaired by a new welding operation. However, the weld zones of the cap and of the collar are subjected to high levels of thermal stress on each welding operation, and that may shorten their lifetime.